Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$199.42	12.250%	$223.849	$223.85	$223.85	$223.80
Purchase #2	$100.53	6.696%	$107.2615	$107.26	$107.25	$107.30
Purchase #3	$92.66	10.605%	$102.4866	$102.49	$102.50	$102.50
Purchase #4	$85.85	8.506%	$93.1524	$93.15	$93.15	$93.20
Purchase #5	$132.34	13.711%	$150.4851	$150.49	$150.50	$150.50
Purchase #6	$129.27	10.716%	$143.1226	$143.12	$143.10	$143.10
Purchase #7	$88.28	13.467%	$100.1687	$100.17	$100.15	$100.20
7 purchase totals =	$828.35		$920.5259	$920.53	$920.50	$920.60